Broadband Wireless Access: Perspectives and Performance.

摘要

This dissertation studies broadband Wireless Internet access from three different perspectives: historical, user-oriented, and network-oriented. Key trends, advances, and challenges are identified and analyzed, providing a basis for suggested performance improvements related to each perspective.;For the user perspective, this dissertation presents an empirical case study of a commercially-available broadband wireless Internet access technology (WiMAX). WiMAX promises high data rates and long-range access for wireless users, and is one of the first to offer both of these features within the same technology. Experimental measurements are used to assess the typical performance that an average user would perceive for both throughput and delay using common Internet applications. Several insights are offered on how to configure TCP to improve performance in WiMAX networks, and which network applications can be expected to perform well and which may face challenges. A proper choice of TCP variant can boost throughput by 15% on the uplink, and reduce the retransmission rate by an order of magnitude. Disabling TCP window auto-tuning can reduce the retransmission rate on the downlink by a factor of four, and on the uplink by 35%.;From the network perspective, this work examines how to use the constrained wireless medium more efficiently. Redundant Traffic Elimination (RTE), known commercially as WAN Optimization, has been traditionally applied to high-bandwidth wired backbone links for ISPs. The RTE approach is explored for use in wireless access networks, a domain in which its usage seems particularly apropos. In addition to improving the effectiveness of RTE by up to 50% in general for wired and wireless environments, it is demonstrated that the benefits of RTE are even greater in WLAN scenarios than in traditional wired networks. The RTE savings are 50-80% for some individual wireless users.;While the wireless performance gap cannot be completely eliminated, this dissertation studies practical approaches to reduce its impact, and quantifies their effectiveness.;The historical perspective views Wireless Internet access through the evolution of wireless technologies, applications, and data traffic from 1998 to 2008. While mainstream wireless technologies achieved a 200-fold increase in data rates over this period of time, the main challenge that still remains is the performance difference between wired and wireless technologies. This "wireless performance gap" is identified as a pervasive trend, and it is the key motivator for the rest of the dissertation.